1. Field of the Invention
The present invention relates to RF receiving coils for magnetic resonance imaging (MRI). More specifically, the invention relates to RF receiving coils incorporating high temperature superconductor (HTS) tapes.
2. Description of the Related Art
The receiver coil in an MRI device receives the signal emitted from the sample that is later converted into a 2-D image or 3-D model of the sample. The receiver coil usually sits inside the magnet and the gradient coils of the MRI device. Receiver coils are normally made of copper wire windings that exhibit a substantial resistance relative to the electrical resistance of the superconductor coils of the magnet or the gradient coils. It is believed that receiver coils employing superconductor materials would result in a higher Quality-factor and better MRI quality.
Receiver coils made of HTS thin films have been fabricated and shown to exhibit a higher quality factor. Ma et al., “Superconducting MR Surface Coils for Human Imaging,” Proc. Mag. Res. Medicine, 1, 171 (1999), herein incorporated by reference, describes a surface receiving coil incorporating HTS thin film. The rigid substrate of the wafer supporting the HTS thin film, however, limits the geometry of the receiving coil to a surface coil configuration.
Hill, “Improved sensitivity of NMR spectroscopy probes by use of high-temperature superconductive detection coils,” IEEE Transactions on Applied Superconductivity, Vol. 7, No. 2 (1977), herein incorporated by reference, describes a detection coil incorporating HTS thin film and reported that the increase in quality factor was partially offset by the lower filling factor of the thin film coil.
The restrictions caused by the rigid HTS film substrate further limits the ability to handle a variety of imaging situations that frequently arise. It is not uncommon to use a variety of coil configurations depending on the sample and the desired information from the MRI scan. For example, a birdcage coil is preferred for imaging the head and brain whereas a single turn coil may be more appropriate for an extremities such as the breasts and the wrist. Furthermore, manufacture of HTS thin films usually require semiconductor-manufacturing techniques that increase the cost of the coil and are limited by the maximum wafer size that the process equipment can handle.
Therefore, there remains a need for a receiver coil having a large quality factor with sufficient flexibility to form the various receiver coil configurations used in present day MRI practice that can be manufactured at low cost.